I'd give it a C.
The intermixing of the Dillinger story and the Purvis/FBI story did not work, IMO. Too much time was spent on the Purvis/FBI story which was simply uninteresting and Christian Bale's acting is about as interesting as watching a dog scratch itself. More time needed to be spent on the actual characters who were the public enemies -- we needed to know more about what made them tick, what drew them together, etc.
I also did not like the "Intro to Cinematography 101: Class will use every form of film photography possible in 2 hours" class. Ugh, from steady cam to sepia to yellow filter to weird angles that did nothing for the story.
The only reason I gave it a C was because Depp and Cotillard gave it their best.